Javascript and the Webviewer

Many long-term FileMaker developers seem to be somewhat apprehensive of using Javascript and the functionality it might bring to FileMaker apps as there can seem like a lot to learn and no-one seems quite sure where to start.

There is some need for entry- and mid-level sessions to sit alongside Todd's NodeJS server stuff to introduce how to use Javascript in the Webviewer, methods of using another library, simple Javascript scripting all the way up to techniques like using d3 or other visualisation libraries to provide dashboard or other chart/graph data.

The Webviewer now contains a whole other calculation engine inside it, so how does information get into it, adn importantly how can callbacks get the transformed data or slections/ choices out again?